Patent application title: LED LIGHTING UNIT

Abstract:

An LED lighting unit can be configured to have a high color rendering for
which color temperature can adjust itself to be close to a natural color.
The LED lighting unit can be composed of three light sources that
respectively include a blue LED and a different phosphor. A first light
source can emit light having a color temperature located substantially on
a blackbody locus, a second light source can emit light having a higher
color temperature than that of the first light source and located
substantially on the blackbody locus, and a third light source can emit a
green or yellow light. A mixture of the light can be located
substantially on the blackbody locus by controlling a beam ratio of the
mixed light having contiguous wavelength components. Therefore, the LED
lighting unit can emit a light having a high color rendering that can
maintain a uniform color within a radiation range.

Claims:

1. An LED lighting unit comprising:a first light source including a blue
LED configured to emit blue light and a phosphor material configured to
wavelength-convert at least a part of the blue light emitted from the
blue LED to red wavelength light and green wavelength light, the phosphor
material configured to emit more red wavelength light than green
wavelength light, and the first light source configured to emit light
having a color temperature located substantially on a blackbody locus;a
second light source including a blue LED configured to emit blue light
and a second phosphor material configured to wavelength-convert at least
a part of the blue light emitted from the blue LED to red wavelength
light and green wavelength light, the second phosphor material configured
to emit more green wavelength light than red wavelength light, and the
second light source configured to emit light having a higher color
temperature substantially on the blackbody locus than a color temperature
of light emitted from the first light source;a third light source
including a blue LED configured to emit blue light and a third phosphor
material configured to wavelength-convert at least a part of the blue
light emitted from the blue LED to at least one of a green wavelength
light and a yellow wavelength light, and the third light source
configured to emit light located within at least one of a green color
area and a yellow color area in an xy chromaticity diagram; anda lens
located in a direction of light-emission of light emitted from the first
light source, the second light source and the third light source, and the
lens being configured to control a mixture of the light emitted from the
first light source, the second light source and the third light source.

2. The LED lighting unit according to claim 1, wherein the light emitted
from the first light source has a color temperature of substantially
2,800 K, the light emitted from the second light source has a color
temperature of substantially 7,000 K, and the light emitted from the
third light source is located within a green color area in the xy
chromaticity diagram.

3. The LED lighting unit according to claim 2, wherein the light emitted
from each of the first light source, the second light source and the
third light source maintains an emission intensity of more than 20
percent of a maximum emission intensity of a respective one of the first
light source, the second light source and the third light source when
emitting light within a wavelength range of from 450 nm to 600 nm.

4. The LED light unit according to claim 1, wherein the light emitted from
the first light source has a color temperature of substantially 2,000 K,
the light emitted from the second light source has a color temperature of
substantially 7,000 K, and the light emitted from the third light source
is located within a green color area in the xy chromaticity diagram.

5. The LED lighting unit according to claim 4, wherein the light emitted
from each of the first light source, the second light source and the
third light source maintains an emission intensity of more than 20
percent of a maximum emission intensity of a respective one of the first
light source, the second light source, and the third light source when
emitting light within a wavelength range of from 470 nm to 660 nm.

6. The LED lighting unit according to claim 1, further comprising:a first
power supply for controlling a driving current to the first light source,
a second power supply for controlling a driving current to the second
light source, and a third power supply for controlling a driving current
to the third light source, wherein both the first power supply and the
second power supply control a beam ratio of light emitted from the first
light source to light emitted from the second light source, and the third
power supply controls a beam ratio of light emitted from the third light
source to both light emitted from the first light source and light
emitted from the second light source.

7. The LED lighting unit according to claim 2, further comprising:a first
power supply for controlling a driving current to the first light source,
a second power supply for controlling a driving current to the second
light source and a third power supply for controlling a driving current
to the third light source, wherein both the first power supply and the
second power supply control a beam ratio of light emitted from the first
light source to light emitted from the second light source, and the third
power supply controls a beam ratio of light emitted from the third light
source to both light emitted from the first light source and light
emitted from the second light source.

8. The LED lighting unit according to claim 3, further comprising:a first
power supply for controlling a driving current to the first light source,
a second power supply for controlling a driving current to the second
light source and a third power supply for controlling a driving current
to the third light source, wherein both the first power supply and the
second power supply control a beam ratio of light emitted from the first
light source to light emitted from the second light source, and the third
power supply controls a beam ratio of light emitted from the third light
source to both light emitted from the first light source and light
emitted from the second light source.

9. The LED lighting unit according to claim 4, further comprising:a first
power supply for controlling a driving current to the first light source,
a second power supply for controlling a driving current to the second
light source and a third power supply for controlling a driving current
to the third light source, wherein both the first power supply and the
second power supply control a beam ratio of light emitted from the first
light source to light emitted from the second light source, and the third
power supply controls a beam ratio of light emitted from the third light
source to both light emitted from the first light source and light
emitted from the second light source.

10. The LED lighting unit according to claim 5, further comprising:a first
power supply for controlling a driving current to the first light source,
a second power supply for controlling a driving current to the second
light source and a third power supply for controlling a driving current
to the third light source, wherein both the first power supply and the
second power supply control a beam ratio of light emitted from the first
light source to light emitted from the second light source, and the third
power supply controls a beam ratio of light emitted from the third light
source to both light emitted from the first light source and light
emitted from the second light source.

11. The LED lighting unit according to claim 1, wherein a mixture of
light, including light emitted from the first light source, light emitted
from the second light source, and light emitted from the third light
source, has a color temperature located substantially on the blackbody
locus.

12. The LED lighting unit according to claim 2, wherein a mixture of
light, including light emitted from the first light source, light emitted
from the second light source, and light emitted from the third light
source, has a color temperature located substantially on the blackbody
locus.

13. The LED lighting unit according to claim 4, wherein a mixture of
light, including light emitted from the first light source, light emitted
from the second light source, and light emitted from the third light
source, has a color temperature located substantially on the blackbody
locus.

14. The LED lighting unit according to claim 6, wherein a mixture of
light, including light emitted from the first light source, light emitted
from the second light source, and light emitted from the third light
source, has a color temperature located substantially on the blackbody
locus.

15. The LED lighting unit according to claim 7, wherein a mixture of
light, including light emitted from the first light source, light emitted
from the second light source, and light emitted from the third light
source, has a color temperature located substantially on the blackbody
locus.

16. The LED lighting unit according to claim 9, wherein a mixture of
light, including light emitted from the first light source, light emitted
from the second light source, and light emitted from the third light
source, has a color temperature located substantially on the blackbody
locus.

17. An LED lighting unit comprising:a first light source including a blue
LED configured to emit blue light and a phosphor configured to
wavelength-convert at least a part of the blue light emitted from the
blue LED to red wavelength light and green wavelength light, the phosphor
configured to emit more red wavelength light than green wavelength
light;a first power supply for controlling a driving current to the first
light source;a second light source including a blue LED configured to
emit blue light and a second phosphor material configured to
wavelength-convert at least a part of the blue light emitted from the
blue LED to red wavelength light and green wavelength light, the second
phosphor material configured to emit more green wavelength light than red
wavelength light;a second power supply for controlling a driving current
to the second light source;a third light source including a blue LED
configured to emit blue light and a third phosphor material configured to
wavelength-convert at least a part of the blue light emitted from the
blue LED to at least one of a green wavelength light and a yellow
wavelength light;a third power supply for controlling a driving current
to the third light source; anda lens located in a direction of
light-emission of light emitted from the first light source, the second
light source and the third light source, and the lens being configured to
control a mixture of the light emitted from each of the first light
source, the second light source and the third light source, wherein both
the first power supply and the second power supply control a beam ratio
of light emitted from the first light source to light emitted from the
second light source, and the third power supply controls a beam ratio of
light emitted from the third light source to both light emitted from the
first light source and light emitted from the second light source.

18. The LED lighting unit according to claim 17, wherein the mixture of
the light emitted from the first light source, the second light source,
and the third light source has a color temperature located substantially
on a blackbody locus.

19. The LED lighting unit according to claim 17, wherein both light
emitted from the first light source and light emitted from the second
light source have color temperatures located substantially on a blackbody
locus.

20. The LED lighting unit according to claim 19, wherein a mixture of
light emitted from the first light source, the second light source, and
the third light source has a color temperature located substantially on a
blackbody locus.

21. The LED lighting unit according to claim 17, wherein the phosphor
material is a mixture of red phosphor wavelength converting material and
green phosphor wavelength converting material, and the second phosphor
material is a mixture of red phosphor wavelength converting material and
green phosphor wavelength converting material.

22. The LED lighting unit according to claim 1, wherein the phosphor
material is a mixture of red phosphor wavelength converting material and
green phosphor wavelength converting material, and the second phosphor
material is a mixture of red phosphor wavelength converting material and
green phosphor wavelength converting material.

Description:

[0001]This application claims the priority benefit under 35 U.S.C. §
119 of Japanese Patent Application No. 2007-217318 filed on Aug. 23, 2007
and Japanese Patent Application No. 2007-294459 filed on Nov. 13, 2007,
both of which are hereby incorporated in their entireties by reference.

BACKGROUND

[0002]1. Field

[0003]The presently disclosed subject matter relates to LED lighting
units, and more particularly to LED lighting units having a high color
rendering of which a color temperature can arbitrarily adjust such that
it is close to a natural color wherein the lighting unit also has a
simple structure.

[0004]2. Description of the Related Art

[0005]Various LED lighting units that include LEDs as a light source have
been developed in recent years. One reason is that LEDs may be a
favorable light source with respect to saving energy, environmental
problems, etc. In addition, LEDs can emit variously-colored lights while
the structure of the LED can be thin and small in size.

[0006]A method for emitting white light by using LEDs as a light source
will now be described. An LED lighting unit for emitting white light is
composed of a red LED, a green LED and a blue LED as a light source. The
LED lighting unit can emit white light by additive color mixture in which
red, green and blue light of the three additive primary colors are mixed
with respect to each other.

[0007]A conventional LED lighting unit that emits white light by additive
color mixture, for example, is disclosed in Patent Document No. 1
(Japanese Patent Application Laid Open JP2001-184910). An LED lighting
unit disclosed in Patent Document No. 1 can emit white light by
controlling each beam ratio of red, green and blue lights and mixing
their lights with respect to one another.

[0008]Specifically, a red LED having both a peak wavelength λp of
605 nm to 635 nm and a half bandwidth Δλ of 15 nm to 60 nm in
emission spectrum, a green LED having both a peak wavelength λp of
530 nm to 570 nm and a half bandwidth Δλ of 20 nm to 60 nm in
emission spectrum and a blue LED having both a peak wavelength λp
of 450 nm to 490 nm and a half bandwidth Δλ of 15 nm to 70 nm
in emission spectrum are used as light sources for the LED lighting unit.

[0009]In this case, the LED lighting unit can emit various types of white
lights having both a correlated color temperature and a general color
rendering index by changing each beam ratio of red, green and blue
lights. FIG. 11 is a spectrum distribution diagram showing a spectrum of
mixed white light made according to the conventional method of additive
color mixture.

[0010]A white light A shown in FIG. 11 has both correlated color
temperature of 6,500 K and general color rendering index Ra of 95.2 by
the additive color mixture in which each beam ratio of a red light having
both a peak wavelength λp of 620 nm and a half bandwidth
Δλ of 16.1 nm in emission spectrum, a green light having both
a peak wavelength λp of 550 nm and a half bandwidth Δλ
of 48.0 nm in emission spectrum, and a blue light having both a peak
wavelength λp of 470 nm and a half bandwidth Δλ of 68.8
nm in emission spectrum, is 20.67, 54.17 and 25.16 percent, respectively.

[0011]A white light B shown in FIG. 11 has both correlated color
temperature of 5,000 K and general color rendering index Ra of 94.4 by
the additive color mixture in which each beam ratio of the red, green and
blue lights is 22.88, 57.89 and 19.24 percent, respectively. A white
light C shown in FIG. 11 has both correlated color temperature of 3,000 K
and general color rendering index Ra of 91.3 by the additive color
mixture in which each beam ratio of the red, green and blue lights is
32.12, 59.35 and 8.24 percent, respectively.

[0012]Another method for emitting white light by using LEDs as a light
source will now be given. Another LED lighting unit for emitting white
light is composed of a blue LED as a light source and at least one
phosphor for wavelength-converting a part of blue light emitted from the
blue LED.

[0013]For instance, by using the blue light emitted from the blue LED and
red and green lights that are made by converting a wavelength of blue
light emitted from the blue LED, the LED lighting unit can emit white
light by an additive color mixture in which red, green and blue light of
the three additive primary colors are mixed with respect to each other.

[0014]When the red light is made by the blue LED and a phosphor, the blue
light emitted from the blue LED is converted to a wavelength of red light
by exciting a red phosphor with the blue light. Similarly, when the green
light is made by the blue LED and a phosphor, a green phosphor is excited
by the blue light emitted from the blue LED and the blue light is
converted to a wavelength of green light. Thus, the LED lighting unit
includes a blue LED as a light source and red and green phosphors for
converting the blue light emitted from the blue LED into red and green
wavelength light.

[0015]Another conventional LED lighting unit that emits white light by the
above-described additive color mixture, for example, is disclosed in
Patent Document No. 2 (Japanese Patent Application Laid Open
JP2002-60747). An LED lighting unit disclosed in Patent Document No. 2
can emit white light by controlling each beam ratio of a blue light
emitted from a blue LED and red and green light that is
wavelength-converted from the blue light via phosphors and by mixing
their light with respect to each another.

[0016]Specifically, the LED lighting unit includes a blue LED having a
peak wavelength λp of 460 nm and a mixture phosphor including both
a red phosphor that is composed of SrS:Eu and a green phosphor that is
composed of SrGa2S4:Eu. The mixture phosphor allows a part of
the blue light emitted from the blue LED to convert to red and green
light, and therefore the LED lighting unit can emit white light by the
additive color mixture in which a non-converted blue light and
wavelength-converted red and green light are mixed with respect to each
other.

[0017]In this case, the LED lighting unit can emit various types of white
light having both a correlated color temperature and a general color
rendering index by changing each beam ratio of red, green and blue light,
such as by controlling a quantity of blue light emitted from the blue LED
and each quantity of red and green phosphors, etc. FIG. 12 is a spectrum
distribution diagram showing a spectrum of mixed white light made
according to the above-described other conventional method of additive
color mixture.

[0018]For instance, a white light D shown in FIG. 12 has both correlated
color temperature of 3,000 K and general color rendering index Ra of 94.
Similarly, white lights E, F and G shown in FIG. 12 have both correlated
color temperature of 3,800 K, 4,400K and 4,900K and general color
rendering index Ra of 94, 94 and 92, respectively.

[0020]As described above, the method for emitting white light by using
red, green and blue LEDs is disclosed in Patent Document No. 1. However,
the LED lighting unit disclosed in Patent Document No. 1 may emit all
color lights including white light by controlling each beam ratio of red,
green and blue light and mixing the different wavelength light with
respect to one another.

[0021]More specifically, the above-described all color lights means all
colors that are located within a triangle of an xy chromaticity diagram
in which three apexes are each of light emitted from the red, green and
blue LEDs. Vector synthesis of the three single wavelengths can result in
emitting all the color lights because the red, green and blue LEDs have
spectrum distributions close to the respective single wavelengths.

[0022]However, each emission spectrum of red, green and blue light emitted
from the LEDs of the above-described LED lighting unit has a narrow half
bandwidth, respectively. In addition, each emission spectrum of red,
green and blue light cannot maintain a contiguous wavelength area between
each emission spectrum thereof due to each separate wavelength component
thereof.

[0023]Thus, for example, when controlling the white light by an additive
color mixture in which red, green and blue light of the three additive
primary colors are mixed with respect to each other, and when emitting
the mixture light to the outside via a lens, the mixture light may cause
each separate area of wavelength components at a contoured part of
radiation range because a refractive index of lens varies from each
wavelength component of red, green and blue light. Consequently, it may
be difficult for the conventional method to maintain a uniform color
within the whole radiation range.

[0024]To help solve the problem, the LED lighting unit uses an optical
mixing structure that may be a relatively complex optical system. In this
case, the optical mixing structure may need a large size of LED lighting
unit because of each alignment of the LEDs, each long light-path, etc. In
addition, when at least one peak wavelength of the emission spectrums of
red, green and blue light shifts, the change of noncontiguous wavelength
may cause a large fluctuation of general color rendering index Ra in the
mixed color light.

[0025]Moreover, each beam of red, green and blue light may be small
because each integration value of spectrum components of a respective
light is small. Especially, each beam of red and blue light having low
luminosity factors may extremely decrease with respect to a beam of green
light having a high luminosity factor. Thus, it may be difficult for the
LED lighting unit to emit brightly due to a low beam of mixed color
light.

[0026]Likewise, the other method for emitting white light by controlling
each beam ratio of a blue light emitted from a blue LED and red and green
light that is wavelength-converted from the blue light can have similar
problems as referenced with regard to the above-described method.

[0027]That is to say, because the blue light emitted from the blue LED and
the red and green light that is wavelength-converted from the blue light
are mixed with respect to each other, the mixture light emitted to the
outside via a lens may cause separation of each area of the wavelength
components at a contoured part of a radiation range because a refractive
index of lens varies from each wavelength component of red, green and
blue light. Thus, the other method may also be difficult to maintain a
uniform color within the whole radiation range.

[0028]In addition, the other method may be difficult to control peak
wavelengths of emission spectrum of red and green light within a normal
range of variation via the mixture phosphor. When a peak wavelength of
blue light emitted from the blue LED shifts, all the peak wavelengths of
light shift and therefore the changes of wavelengths may cause a
fluctuation of general color rendering index Ra in the mixed color light.

[0029]The disclosed subject matter has been devised to consider the above
and other problems and characteristics. Thus, embodiments of the
disclosed subject matter can include LED lighting units having a high
brightness and a high color rendering that can maintain a uniform color
within the whole radiation range.

[0030]Furthermore, the disclosed subject matter can also include an LED
lighting unit of which a color temperature of emission color is
configured to arbitrarily adjust close to a natural color such as
sunlight, and can reduce or change associated problems and
characteristics of the conventional lighting units and methods.

SUMMARY

[0031]The presently disclosed subject matter has been devised in view of
the above and other problems and characteristics. An aspect of the
disclosed subject matter includes LED lighting units that can emit
various color lights including white light.

[0032]According to another aspect of the disclosed subject matter, an LED
lighting unit can include: a first light source including a blue LED and
a mixture phosphor for wavelength-converting a part of blue lights
emitted from the blue LED to wavelengths of red and green lights, the
mixture phosphor be configured to emit the wavelength of red light more
than the wavelength of green light; a second light source including a
blue LED and a mixture phosphor for wavelength-converting a part of blue
lights emitted from the blue LED to wavelengths of red and green lights,
the mixture phosphor be configured to emit the wavelength of green light
more than the wavelength of red light; and a third light source including
a blue LED and a phosphor for wavelength-converting a part of blue lights
emitted from the blue LED to a wavelength of green light or a phosphor
for wavelength-converting a part of blue lights emitted from the blue LED
to a wavelength of yellow light. The first light source can emit a light
having a color temperature located on substantially blackbody locus, the
second light source can emit a light having a higher color temperature on
substantially blackbody locus than the color temperature of light emitted
from the first light source and the third light source can emit a light
that is located within a green color area or a yellow color area in xy
chromaticity diagram. In addition, a lens can locate towards a direction
of light-emission of the lights emitted from the first light source, the
second light source and the third light source, and the lens can be
configured to control a mixture light of their lights.

[0033]In the above described exemplary LED lighting unit, the LED lighting
unit can further include: a first power supply for controlling a driving
current of the first light source; a second power supply for controlling
a driving current of the second light source; and a third power supply
for controlling a driving current of the third light source. Both the
first power supply and the second power supply can control the beam ratio
of the light emitted from the first light source to the light emitted
from the second light source and the third power supply can control the
beam ratio of the light emitted from the third light source to both the
light emitted from the first light source and the light emitted from the
second light source

[0034]According to the above-described exemplary LED lighting unit, the
LED lighting unit can have the mixture light located on substantially
blackbody locus by controlling each beam ratio of the above-described
three lights having contiguous wavelength components. Therefore, the LED
lighting unit can emit a light having a high color rendering that can
maintain a uniform color within a radiation range and also a color
temperature thereof can arbitrarily be adjusted a close light to a
natural color like sunlight with a simple structure.

[0035]According to another aspect of the disclosed subject matter, an LED
lighting unit can include: a first light source including a blue LED and
a mixture phosphor for wavelength-converting a part of blue lights
emitted from the blue LED to wavelengths of red and green lights, the
mixture phosphor be configured to emit the wavelength of red light more
than the wavelength of green light; a first power supply for controlling
a driving current of the first light source; a second light source
including a blue LED and a mixture phosphor for wavelength-converting a
part of blue lights emitted from the blue LED to wavelengths of red and
green lights, the mixture phosphor be configured to emit the wavelength
of green light more than the wavelength of red light; a second power
supply for controlling a driving current of the second light source; a
third light source including a blue LED and a phosphor for
wavelength-converting a part of blue lights emitted from the blue LED to
a wavelength of green light or a phosphor for wavelength-converting a
part of blue lights emitted from the blue LED to a wavelength of yellow
light; a third power supply for controlling a driving current of the
third light source; and a lens located towards a direction of
light-emission of lights emitted from the first light source, the second
light source and the third light source, and the lens be configured to
control a mixture light of the three lights. Moreover, both the first
power supply and the second power supply can control the beam ratio of
the light emitted from the first light source to the light emitted from
the second light source and the third power supply can control the beam
ratio of the light emitted from the third light source to both the light
emitted from the first light source and the light emitted from the second
light source.

[0036]In the above-described exemplary LED lighting unit, the LED lighting
unit can emit various color lights that are located within a triangle of
xy chromaticity diagram in which three apexes are each of their lights
emitted from the first light source, the second light source and the
third light source by controlling each beam ratio of the three lights
having contiguous wavelength components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]These and other characteristics and features of the disclosed
subject matter will become clear from the following description with
reference to the accompanying drawings, wherein:

[0038]FIG. 1 is a side cross-section summary view showing a structure for
a first exemplary embodiment of an LED lighting unit made in accordance
with principles of the disclosed subject matter;

[0039]FIG. 2 is a spectrum distribution diagram showing a spectrum of
light L emitted from a first light source 1a of the LED lighting unit
shown in FIG. 1;

[0040]FIG. 3 is a spectrum distribution diagram showing a spectrum of
light W emitted from a second light source 1b of the LED lighting unit
shown in FIG. 1;

[0041]FIG. 4 is a spectrum distribution diagram showing a spectrum of
light G emitted from a third light source 1c of the LED lighting unit
shown in FIG. 1;

[0042]FIG. 5 is a uv chromaticity diagram showing a relation between the
lights L, W and G and a mixture light LWG mixed by the light sources 1a,
1b and 1c of the LED lighting unit shown in FIG. 1 along with blackbody
locus;

[0043]FIG. 6 is a spectrum distribution diagram showing a spectrum of the
mixture light LWG having color temperature of 5,000 K in the LED lighting
unit shown in FIG. 1;

[0044]FIG. 7 is a side cross-section summary view showing a structure for
a second exemplary embodiment of an LED lighting unit made in accordance
with principles of the disclosed subject matter;

[0045]FIG. 8 is a spectrum distribution diagram showing a spectrum of a
light L emitted from a first light source 1a of the LED lighting unit
shown in FIG. 7;

[0046]FIG. 9 is a spectrum distribution diagram showing a spectrum of a
light Y emitted from a third light source 1c of the LED lighting unit
shown in FIG. 7;

[0047]FIG. 10 is a uv chromaticity diagram showing a relation between the
lights L, W and Y and a mixture light LWY mixed by the light sources 1a,
1b and 1c of the LED lighting unit shown in FIG. 7 along with blackbody
locus;

[0048]FIG. 11 is a spectrum distribution diagram showing a spectrum of
mixed white light according to a conventional method of additive color
mixture; and

[0049]FIG. 12 is a spectrum distribution diagram showing a spectrum of
mixed white light according to another conventional method of additive
color mixture.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0050]The first exemplary embodiment of the disclosed subject matter will
now be described in detail with reference to FIGS. 1 to 6. FIG. 1 is a
cross-sectional summary view showing a structure for a first exemplary
embodiment of an LED lighting unit made in accordance with principles of
the disclosed subject matter.

[0051]The LED lighting unit can include a first light source 1a, a second
light source 1b and a third light source 1c, of which spectrum
distributions are respectively different. Each of the light sources 1a,
1b and 1c can be configured with a blue LED emitting a blue light having
a peak wavelength of 450 nm to 480 nm. In addition, each of the light
sources 1a, 1b and 1c can include phosphors 3a, 3b and 3c, respectively,
and can be configured to emit a different color light from the blue light
by exciting each of the phosphors 3a, 3b and 3c with the blue light.

[0052]The phosphor 3a can include both a red phosphor emitting a red light
that is wavelength-converted by exciting the red phosphor with the blue
light and a green phosphor emitting a green light that is
wavelength-converted by exciting the green phosphor with the blue light.
The mixture ratio of the red phosphor to the green phosphor can be
configured to emit more red light than green light.

[0053]The phosphor 3b can also include both a red phosphor for emitting a
wavelength-converted red light and a green phosphor for emitting a
wavelength-converted green light. However, the mixture ratio of the red
phosphor to the green phosphor can be configured to emit more green light
than red light. The phosphor 3c can include a green phosphor for emitting
a wavelength-converted green light.

[0054]The above-described red phosphor can include SrS:Eu and the like,
and the green phosphor can include SrGa2S4:Eu, etc. Therefore,
each of the light sources 1a, 1b and 1c can emit light L, W and G
described later in detail, respectively. In addition, a lens 4 can be
located in a direction of light-emission of the lights L, W and G in
order to control a light distribution of mixture light LWG which is mixed
light by additive color mixture. The lights L, W and G and the mixture
light LWG will now be described in more detail in turn.

[0055]The light L emitted from the first light source 1a can include both
the blue light emitted from the blue LED 2 and a light
wavelength-converted by exciting the phosphor 3a with a part of the blue
light emitted from the blue LED 2. Thus, the light L can have a different
spectrum distribution from that of the blue light emitted from the blue
LED 2.

[0056]FIG. 2 is a spectrum distribution diagram showing a spectrum of the
light L emitted from the first light source 1a. The light L can include a
contiguous wavelength component of approximately 420 nm to 830 and can
maintain an emission intensity of more than 20 percent of maximum
emission intensity within a broad range of around 450 nm to 710 nm, as
shown in FIG. 2.

[0057]In addition, the light L can have a high color rendering index that
is close to that of a typical bulb color having a color temperature of
2,800 K on a color temperature coordinate. The reasons are that the first
light source 1a includes both the blue LED 2 and the phosphor 3a, which
includes both the red phosphor for converting a blue light to a
wavelength of red light and the green phosphor for converting a blue
light to a wavelength of green light. The mixture ratio of the red
phosphor and the green phosphor can be configured to emit more red
wavelength light than green wavelength light.

[0058]The light W that is emitted from the second light source 1b can also
include both blue light emitted from the blue LED 2 and a light that is
wavelength-converted by exciting phosphor 3b with a part of the blue
light emitted from the blue LED 2. Thus, the light W can also have a
different spectrum distribution from that of the blue light emitted from
the blue LED 2.

[0059]FIG. 3 is a spectrum distribution diagram showing a spectrum of the
light W emitted from the second light source 1b. The light W can include
a contiguous wavelength component of approximately 420 nm to 800 and can
maintain an emission intensity of more than 20 percent of maximum
emission intensity within a broad range of around 450 nm to 660 nm, as
shown in FIG. 3.

[0060]In addition, the light W can have a high color rendering index that
is close to that of a white color tone corresponding to a color
temperature of 7,000 K on a color temperature coordinate. The reasons are
that the second light source 1b includes both the blue LED 2 and the
phosphor 3b, which includes both the red phosphor for converting blue
light to red light and the green phosphor for converting blue light to
green light. The mixture ratio of the red phosphor and the green phosphor
is configured to emit more green light than red light.

[0061]Furthermore, the light G emitted from the third light source 1c can
also include both the blue light emitted from the blue LED 2 and light
that is wavelength-converted by exciting the phosphor 3c with part of the
blue light emitted from the blue LED 2. Thus, the light G can also have a
different spectrum distribution from that of the blue light emitted from
the blue LED 2.

[0062]FIG. 4 is a spectrum distribution diagram showing a spectrum of the
light G emitted from the third light source 1c. The light G can include a
contiguous wavelength component of approximately 420 nm to 780 and can
maintain an emission intensity that is more than 20 percent of a maximum
emission intensity and within a wide range of around 450 nm to 620 nm, as
shown in FIG. 4.

[0063]The light G can have a green color tone in an xy chromaticity
diagram, in which the x value is approximately 0.276 and the y value is
around 0.423. The reasons are that the third light source 1c includes
both the blue LED 2 and phosphor 3c, which includes the green phosphor
for converting blue light to green light by exciting the phosphor with
the blue light.

[0064]The above-described lights L, W and G can maintain an emission
intensity of more than 20 percent of a maximum emission intensity and
within a wavelength range of at least around 450 nm to 600 nm. FIG. 5 is
a uv chromaticity diagram showing a relation between the lights L, W and
G and a mixture light LWG mixed with the light emitted from the light
sources 1a, 1b and 1c of the LED lighting unit, along with blackbody
locus.

[0065]As shown in FIG. 5, both the light L having color temperature of
2,800 K and the light W having color temperature of 7,000K can be located
on substantially blackbody locus. However, the light G having an x value
of approximately 0.276 and a y value of around 0.423 in xy chromaticity
diagram can be located outside of the blackbody locus in the uv
chromaticity diagram.

[0066]According to the disclosed subject matter, the mixture light LWG of
the above-described lights L, W and G can be used for an LED lighting
unit without an adjustment in some applications. However, the LED light
unit can emit various color lights that are located within a triangle of
xy chromatic coordinate in which three apexes are the lights L, W and G
by changing the beam ratio of the lights L, W and G emitted from the
respective light sources 1a, 1b and 1c.

[0067]Because the additive color mixture light LWG of the lights L, W and
G can continuously be moved on blackbody locus by changing each beam
ratio between the lights L, W and G, the LED lighting unit can emit a
light that is close to a natural color, such as sunlight. A method for
continuously moving the mixture light LWG on the blackbody locus will now
be described in detail with reference to FIG. 5.

[0068]The LED light unit can include a first power supply for controlling
a driving current of the blue LED 2 of the first light source 1a, a
second power supply for controlling a driving current of the blue LED 2
of the second light source 1b and a third power supply for controlling a
driving current of the blue LED 2 of the third light source 1c.

[0069]The beam ration of the light L to the light W can be changed by
controlling each driving current of the blue LEDs 2 of the light sources
1a and 1b. When changing the beam ratio of the light L to the light W, an
additive color mixture light LW of both the lights L and W can move on a
line L-W, which connects the light L to the light W in the uv
chromaticity diagram.

[0070]More specifically, when supplying only the first light source 1a
with the driving current, the mixture light LW can be emitted at a color
temperature of 2,800 K on the blackbody locus, because the first light
source 1a can emit the light L at a color temperature of 2,800 K on
blackbody locus but the second light source 1b cannot emit the light W
without the driving current.

[0071]Then, if the driving current of the second light source 1b is
gradually increased by the second power supply while the driving current
of the first light source 1a is gradually decreased by the first power
supply, the beam ratio of the light W to the light L can gradually
increase from zero percent and therefore the mixture light LW can move on
the line L-W toward the light W in the uv chromaticity diagram.

[0072]Finally, when supplying only the second light source 1b with the
driving current and not supplying the first light source 1a with a drive
current, the mixture light LW can be emitted at a color temperature of
7,000 K in blackbody locus. This is because the second light source 1b
can emit light W at a color temperature of 7,000 K on the blackbody
locus, but the first light source 1a cannot emit light L because the
driving current is not supplied thereto.

[0073]In this case, the line L-W on which the mixture light LW moves may
be different from the blackbody locus. However, the line L-W can be
located near the blackbody locus. In addition, the beam ration of the
light G to the mixture light LW can be changed by controlling a driving
current of the blue LED 2 of the third light source 1c.

[0074]Moreover, when changing the beam ratio of the light G to the mixture
light LW, the additive color mixture light LWG of both the light G and
the mixture light LW can move on a line LW-G, which connects the light G
to the mixture light LW in the uv chromaticity diagram. Thus, the mixture
light LWG can be located at the intersection of the line LW-G and
blackbody locus by controlling the driving current of the blue LED 2 of
the third light source 1c.

[0075]More specifically, when supplying only both the light sources 1a and
1b with driving currents while maintaining the predetermined beam ratio
of the light L to the light W, the mixture light LW can be emitted on the
line L-W in the uv chromaticity diagram, because the third light source
1c cannot emit the light G without the driving current.

[0076]Then, if the driving current of the third light source 1c is
gradually increased by the third power supply while maintaining the
predetermined beam ratio of the light L to the light W, the beam ratio of
the light G to the mixture light LW can gradually increase from zero
percent. Therefore the mixture light LWG can move on the line LW-G toward
the light G in the uv chromaticity diagram.

[0077]Thus, the mixture light LWG can be located at the intersection of
the line LW-G and the blackbody locus by controlling the driving current
of the blue LED 2 of the third light source 1c. In this case, if the
driving currents of both the light sources 1a and 1b are gradually
decreased while maintaining the predetermined beam ratios of both the
light L to the light W and the light G to the mixture light LW, the
mixture light LWG can move on the line LW-G toward the light G in the uv
chromaticity diagram.

[0078]Finally, when supplying only the third light source 1c with the
driving current and when both the light sources 1a and 1b are not
supplied with drive currents, the mixture light LWG can be emitted at the
light G having an x value of approximately 0.276 and y value of around
0.423 in the xy chromaticity diagram.

[0079]Thus, the LED light unit of this embodiment of the disclosed subject
matter can provide all color lights that are located within a triangle of
chromatic coordinate in which three apexes of color lights are formed by
the first light source 1a, the second light source 1b and the third light
source 1c. In addition, because the above-described mixture light LWG can
be emitted on a blackbody locus within the range between the light L to
the light W, the LED light unit can enjoy a natural light such as
sunlight.

[0080]Results of an exemplary experiment using the LED lighting unit are
shown in the following table 1, in which a relation between color
temperature and both general color rendering index Ra and conversion
efficiency shows when the mixture light LWG moves on the blackbody locus
of 2,800 K to 7,000K in the uv chromatic coordinate, as shown in FIG. 5.

[0081]The general color rendering index Ra of the mixture light LWG can be
92 at each color temperature from 2,800K to 7,000K. In addition, the
conversion efficiency can be 34 lm/W for each of the color temperature
values from 2,800K to 7,000K, as shown in Table 1. Thus, the LED lighting
unit can have both a high and stable general color rendering index Ra and
favorable conversion efficiency even when an emission color thereof
continuously changes.

[0082]FIG. 6 is a spectrum distribution diagram showing a spectrum of the
mixture light LWG having color temperature of 5,000 K. The mixture light
LWG can include a contiguous wavelength component of approximately 420 nm
to 830 nm and can maintain an emission intensity of more than 20 percent
of a maximum emission intensity within a broad range of around 450 nm to
690 nm, as shown in FIG. 6. Thus, the LED lighting unit can emit white
light having both a high color rendering index and high emission
efficiency.

[0083]As described above, the LED lighting unit can emit the mixture light
LWG having a predetermined color temperature from the outside via the
lens 4. In this case, because the mixture light LWG can maintain an
emission intensity of more than 20 percent of a maximum emission
intensity and within a broad range of around 450 nm to 690 nm, the
mixture light LWG may not cause each separate area of wavelength
component to be discernable at contoured parts of a radiation range.
Thus, the LED light unit can emit a uniform color light within the whole
radiation range.

[0084]When the mixture light LWG is emitted via lens 4 and focused to the
outside, because the mixture light LWG does not generate separate color
light within the radiation range, the LED lighting unit can favorably be
used as a spot light. In addition, the spot light can be structured with
a thin and small size because of the ability to focus the mixture light
LWG with a simple optical structure.

[0085]Furthermore, because the mixture light LWG can include large
integration values of red and blue light having low luminosity factors in
a spectrum thereof, as shown in FIG. 6, the mixture light LWG can be
large and bright and configured for use as a light source for the LED
lighting unit. Thus, the mixture light LWG can result in LED lighting
units having a high brightness and a favorable light distribution.

[0086]It is ideal to locate both of the lights L and W on the blackbody
locus in order to locate the mixture light LWG on blackbody locus.
However, a difference between both of the lights L and W and the
blackbody locus can be within a range, for example, from -0.002 duv to
+0.002 duv, or from -0.005 duv to +0.005 duv, in order to reduce the
driving current of the third light source 1c.

[0087]The light G can have a green color tone in the xy chromaticity
diagram, in which the x value is approximately 0.276 and the y value is
around 0.423 as described above. However, the light G should not be
limited to these xy values, and can be located within a green area in the
xy chromaticity diagram in which the line LW-W can intersect with
blackbody locus.

[0088]The above-described first exemplary embodiment can be useful with
respect to the mixture light LWG having color temperature of 2,800K to
7,000K on the blackbody locus. However, the mixture light LWG may not be
efficiently emitted at a color temperature of less than 2,800K. Thus, the
LED lighting unit using the mixture light LWG may have difficulty in some
cases emitting a light such as a candlelight having color temperature of
around 2,000K, a sunlight at sunup and sundown having color temperature
of approximately 2,500K, etc.

[0089]A second exemplary embodiment of the disclosed subject matter will
now be given with reference to FIGS. 7 to 10. A structure for the second
exemplary embodiment of an LED lighting unit is shown in FIG. 7, wherein
the same or similar elements shown in FIG. 1 are referenced by same
reference numerals. The LED lighting unit can be similar to the LED
lighting unit shown in FIG. 1. Differences between the LED lighting unit
shown in FIG. 7 and the LED lighting unit shown in FIG. 1 can be the
phosphor 3a of the first light source 1a and the phosphor 3c of the third
light source.

[0090]The phosphor 3a of the second exemplary embodiment can also include
both a red phosphor for converting a blue light to a red wavelength light
by exciting the phosphor with the blue light, and a green phosphor for
converting a blue light to a green wavelength light by exciting the
phosphor with the blue light. However, the mixture ratio of the red
phosphor to the green phosphor can be configured to emit more red light
in the second exemplary embodiment than green light as compared to the
first exemplary embodiment.

[0091]FIG. 8 is a spectrum distribution diagram showing a spectrum of the
light L emitted from the first light source 1a of the second exemplary
embodiment. The light L can include a contiguous wavelength component of
approximately 450 nm to 830 and can maintain emission intensity to be
more than 20 percent of a maximum emission intensity and within a broad
range of around 470 nm to 710 nm as shown in FIG. 8.

[0092]Therefore, the light L can have a high color rendering index that is
close to that of a color tone of candlelight having a color temperature
of 2,000 K on a color temperature coordinate. The reasons are that the
first light source 1a includes both the blue LED 2 and the phosphor 3a,
which includes both a red phosphor for converting blue light to a red
wavelength light and a green phosphor for converting blue light to a
green wavelength light. The mixture ratio can be configured to emit more
red wavelength light in the second exemplary embodiment as compared to
green wavelength light as in the first exemplary embodiment.

[0093]On the other hand, the phosphor 3c used in the second exemplary
embodiment can include a yellow phosphor for converting blue light to a
yellow wavelength light by exciting the phosphor with the blue light,
unlike that in the first exemplary embodiment. Thus, the light Y emitted
from the third light source 1c can include both a part of blue light
emitted from the blue LED 2 and yellow light wavelength-converted by
exciting the phosphor 3c with the blue light emitted from the blue LED 2.

[0094]FIG. 9 is a spectrum distribution diagram showing a spectrum of the
light Y emitted from the third light source 1c. The light Y can include a
contiguous wavelength component of approximately 450 nm to 800 and can
maintain an emission intensity of more than 20 percent of a maximum
emission intensity and within a wide range of around 460 nm to 660 nm as
shown in FIG. 9.

[0095]The light Y can have a yellow color tone in an xy chromaticity
diagram, in which the x value is within a range of from approximately
0.35 to 0.45 and the y value is within a range of from around 0.4 to 0.5.
The reasons are that the third light source 1c includes both the blue LED
2 and the phosphor 3c, which includes the yellow phosphor for converting
blue light to a yellow wavelength light by exciting the phosphor with the
blue light.

[0096]FIG. 10 is a uv chromaticity diagram showing a relation between the
lights L, W and Y and a mixture light LWY mixed by the light sources 1a,
1b and 1c along with a blackbody locus. Both the light L having a color
temperature of 2,000 K and the light W having a color temperature of
7,000K can be located substantially on the blackbody locus. However, the
light Y having an x value of approximately 0.35 to 0.45 and a y value of
around 0.4 to 0.5 in the xy chromaticity diagram can be located outside
of the blackbody locus in the uv chromaticity diagram.

[0097]The additive color mixture light LWY of the lights L, W and Y can
also be moved on the blackbody locus by changing each beam ratio between
the lights L, W and Y as shown in paragraph [0066]-[0077] in the first
exemplary embodiment.

[0098]Results of an exemplary experiment using the mixture light LWY are
shown in the following table 2, in which a relation between color
temperature and both general color rendering index Ra and conversion
efficiency shows the mixture light LWY moving on the blackbody locus of
2,000 K to 7,000K in the uv chromatic coordinate as shown in FIG. 10.

[0099]A general color rendering index Ra of the mixture light LWG can all
be 92 at each color temperature from 2,000K to 7,000K. Also, the
conversion efficiency can all be 34 lm/W as shown in Table 2. Thus, the
disclosed subject matter can provide LED lighting units having both a
high and stable general color rendering index Ra and favorable conversion
efficiency even when an emission color thereof continuously changes from
2,000K to 7,000K.

[0100]Because the mixture light LWY in the second exemplary embodiment can
also maintain an emission intensity of more than 20 percent of a maximum
emission intensity within a broad range from around 470 nm to 700 nm, the
mixture light LWY should not cause separation at each area of wavelength
components at contoured parts of a radiation range.

[0101]Thus, the disclosed subject matter can provide an LED lighting unit
having a high color rendering that can maintain a uniform color within
the whole radiation range. In addition, the color temperature can
arbitrarily be adjusted to be close to a natural color between 2,000K and
7,000K on blackbody locus.

[0102]In the above-described embodiments, each number of the light sources
1a, 1b and 1c is described as one light source and the number of LED
therein is also described as one LED. However, their numbers should not
be limited to one light source or one LED. The number can be determined
according to a particular usage, purpose, application, etc. In addition,
the lens 4 is described and depicted as covering all the light sources
with one lens. However, a plurality of lenses can be used so as to cover
each of the light sources or so as to separately cover a plurality of
light sources without departing from the spirit and scope of the
presently disclosed subject matter.

[0103]While there has been described what are at present considered to be
exemplary embodiments of the invention, it will be understood that
various modifications may be made thereto, and it is intended that the
appended claims cover such modifications as fall within the true spirit
and scope of the invention. All conventional art references described
above are herein incorporated in their entirety by reference.